Event-related potential (ERP) electrical activity is to be recorded from normal children, adolescents and young adults aged 6 to 30 using a short-term longitudinal design. This aspect of the experimental protocol is designed to verify the ERP and behavioral findings obtained from the same subjects in a cross-sectional age paradigm. The focus is on endogenous ERP components, whose elicitation is highly dependent on the cognitive structure of the task. The tasks to be used are modifications for ERP recording of experiments designed to study hierarchival levels of cognitve information processing. Three levels of increasing cognitive complexity are used in which subjects must match pictorial stimuli on the basis of whether they are physically identical, share the same name, or are in the same category. These three modes of cognitive processing play highly significant roles in normal cognitive functioning and the automaticity with which they are invoked is known to change with increasing age. It is expected that the structure of the cognitive-related brain potentials will parallel cognitive development. The longitudinal data, in comparison with the cross-sectional data collection, will allow the ultimate assessment of which ERP components follow the course of cognitive development (as assessed by performance on these tasks) and will, in turn, deepen our understanding of the cognitive components of the ERP. The data will be highly relevant to the study of abnormal samples of children, who are characterized by arrests in development or maturational lags.